I. Field of the Invention
This invention relates to a method of very precisely washing super precision devices such as semiconductor devices.
II. Description of the Related Art
General process of producing semiconductor devices comprises a first group of steps for preparing silicon wafers from monocrystalline silicon, a second group of steps for forming a desired pattern on the wafer, and a third group of steps for wiring, forming electrodes and testing the completed devices. Each group of steps includes several to several tens of steps, and washing is generally performed between each of the steps.
The contaminants which may be contaminated in the semiconductor devices during the manufacturing process thereof includes (1) organic materials such as dandruff, skin grime and saliva from the workers, oil such as grinding oil and lubricant, waste thread, paper, photoresist, mist, bacteria in pure water for rinsing, and particles contaminated in reagents used; (2) inorganic materials such as abradings of the wafer, dusts produced by chipping of the wafer, metal particles produced by the abrasion of apparatuses; and (3) elements and ions such as alkali metals, heavy metals, oxygen, carbon, radioactive Na and U.sup.235 ; as well as the bacteria which assimilate the organic additives of the polyvinyl chloride used as the pipings of the apparatus and Na, C, N, P, S and K originating therefrom. Among these, those which are most difficult to wash off are said to be the organic contaminants (1). This is because that most of the organic contaminants are very small and usually have a size of 0.1 .mu.m to 10 .mu.m. Those contaminants with a size less than 0.1 .mu.m are not so rare and some contaminants are of molecular size. Such fine organic contaminants are often firmly bound to the semiconductor devices and are difficult to remove. Recent semiconductor devices are highly integrated and a great number of fine grooves, holes and ribs are three-dimensionally and complicatedly combined. If the organic contaminants enter such fine grooves or holes, it is very difficult to remove the contaminants. This is a cause to degrade the yield of the semiconductor devices, which is currently said to be 20%-60%. The difficulty in removing such a contaminant can be compared to the difficulty in removing several contaminants with a size of a small coin in somewhere in the grooves with a width of 1 cm and a depth of 5 cm among the 1,000,000 grooves formed in a baseball stadium.
The washing of the semiconductor devices is conventionally conducted by washing the devices with super pure water or with an organic solvent such as trichloroethylene. However, fine organic contaminants as described above cannot be well removed by this method. Further, the use of organic solvents as washing liquid is restricted because of the problem of the environment pollution.